Pore-size selective modification of porous materials

ABSTRACT

A method of pore-size selective chemical modification of materials having pores of about 1 to 1,500 nm is disclosed. The resulting novel porous materials are particularly useful as separation media in chromatography, for selective isolation, adsorption and catalysis.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 08/388,721 filed on Feb.15, 1995 now allowed which is a CIP of U.S. Ser. No. 07/964,405, filedOct. 21, 1992, now abandoned.

BACKGROUND OF THE INVENTION

Size selectivity is one of the leading principles of nature. Cellmembranes allow permeation of small molecules in the cell body while thelarge ones are excluded. A similar principle has been adopted in themembrane technology and it is widely used there. Size exclusion is alsoone of the often used methods in chromatographic separations. The firstpaper describing so called "gel filtration," involving the separation ofproteins from salt, dates back to 1959. Further progress in sizeexclusion chromatography was made by Moore, J. C. J. Polym. Sci. A2,842, 1964, who introduced macroporous poly(styrene-co-divinylbenzene)beads and developed gel permeation chromatography.

Porous polymer beads are generally produced by the co-polymerization ofonly a limited number of monomers and crosslinking agents. The broadspectrum of pore surface chemistries available for such beads iscommonly obtained by chemical modification of the basic copolymersrather than by the co-polymerization of a monomer bearing the new group.(Sherrington et al., Syntheses and Separations Using FunctionalPolymers, Wiley, N.Y., 1989.) While in the former process the physicalproperties of the basic matrix remains unchanged and only its surfacemay be modified, in the later the functional monomers are partly buriedinside the matrix and physical properties of the copolymers change whendifferent polymerization feeds are used. Accordingly, the chemicalmodification of polymer beads is more frequent than is the directcopolymerization of functional monomers. For example, strong cation- andall anion-exchange resins are currently commercially produced bychemical modification of styrene-divinylbenzene copolymers, while only aweak cation-exchanger is produced by polymerization of a mixturecontaining acrylic acid.

The extent of modification of a porous polymer is typically controlledby the reaction kinetics, i.e., by concentration of reagent, reactiontime and temperature, diffusion, neighboring group effects, etc. Duringsuch a modification, reaction of groups exposed in the easily availableparts of the porous polymer is preferred. As the reaction proceeds, thegroups located in less accessible parts react to a larger extent untilall groups available are consumed. The kinetic control of the reactionpath allows neither specification of locations that should be modifiednor prevention of the reaction of some groups in defined regions of aporous bead. The method only controls the overall reaction conversion,i.e., the average content of modified groups, without defining thelocation thereof.

A far better approach, however, would be to develop a process to controlnot only the extent of modification but also the location of the groupsundergoing reaction. It is an object of the present invention to do soby development of a porous material containing different size poreswhich pores can be selectively modified to have different surfaceproperties.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a process whichcomprises treating a porous material having reactive groups within someof its pores with a modifying agent of a size which penetrates into onlycertain pores of the porous material, which modifying agent chemicallymodifies or assists in the chemical modification of the reactive groupsonly within the pores so penetrated. The porous material has a varietyof different pore sizes generally ranging from about 1 to 1500 nm andeach porous material has pores of at least two size ranges which areeach substantially homogeneously distributed throughout the material.

As used herein, the term "pores" refers to openings of about 1 to 1,500nm in average diameter which originate from the surface of a body. Theterm "pores" means those openings present, for example, within a porousbead or the like used for chromatographic separations while expresslyexcluding those openings, spaces or interstices which exist between twoor more surfaces of separate elements which form a more complex body, asexists between fibrous elements or the like in a filter or in thestructure of U.S. Pat. No. 5,004,645 and the like.

The surfaces of the pores have surface groups which are reactive groupssuch as epoxy, alcohol, acetal, aldehyde, chloromethyl, thiol, amine,ester, carboxylic acid and anhydride, amide, oxime, imine, hydrazone,enamine, or oxazoline groups. The reactive groups within the poresdetermine the reactivity of the surfaces thereof.

The process of the present invention selectively modifies the pores ofthe porous material by employing a modifying agent which reacts with thereactive groups in certain pores, or catalyzes their reaction withanother reagent, to chemically modify the reactive surface groups todifferent surface groups, thereby changing the surface functionality ofthe pore surface. For example, hydrophilic reactive groups can bechanged to hydrophobic groups and vice-versa, changing the surfacefunctionality of the pore surface.

Selective modification is achieved by using a modifying agent such as acatalyst or reagent which is of a size which permits it to penetrateinto only certain sized pores. Once it penetrates into the pores inwhich it fits, the chemical modification occurs transforming thereactive groups therein to surface groups of a different functionalitythan the original reactive groups. The pores into which the modifyingagent can not penetrate because of size constraints remain unmodified.The resultant porous material contains pores with different surfacesfunctionalities. The material is permeable to air and liquids bothbefore and after modification.

The process of the present invention also includes the preparation ofmaterials possessing different reactive groups in pores of at least twosize ranges by a series of consecutive reactions using modifying agentswith different molecular sizes. In this way, a porous material may beproduced containing two or more different surface functionalitieslocalized in pores of different sizes. For example, the porous materialmay be first modified using a relatively low molecular volume modifyingagent which transforms all accessible groups in substantially all of thepores from one functionality to another functionality, and then anothermodifying agent with a larger molecular volume than the first modifyingagent is used to penetrate only relatively larger pores, therebychanging the functionality therein. In a consecutive fashion, modifyingagents each having relatively larger molecular volumes than the last oneemployed may be used to change the functionalities only in the pores inwhich they fit. While this convergent process may employ an unlimitednumber of different size modifying agents, generally from about 2 to 5and more preferably from about 2 to 3 different size modifying agentsare used. The resultant porous material generally contains pores withabout 2 to 5 and more preferably from about 2 to 3 differentfunctionalities. The convergent process can be reversed by starting witha relatively large modifying agent and gradually decreasing the size ofthe modifying agent in each divergent process step. Alternatively theconvergent and divergent process can be combined using, for example, arelatively small molecular volume catalyst in the first reaction step, arelatively large molecular volume catalyst in the second reaction stepand modifying agents with molecular volumes therebetween the two used inthe first two step in remaining steps. The process variants depend onthe porous material, modifying agent, reactive groups and desiredproduct.

The products produced by the process of the present invention compriseporous materials having at least two different pore size ranges, withthe pores of one size range having surface groups of one functionalityand the pores of another size range having surface groups of a differentfunctionality. For example, pores within the range of 1 up to 5 nm mayhave hydrophilic groups and pores within the range of more than 5 to 50nm may have hydrophobic groups. Numerous other combinations are possiblewith the specific different sizes of the pores being of littleimportance.

Materials produced by the process of the present invention are useful asseparation media in chromatography, as membranes, diagnostic materials,medical devices such as hemoperfusion columns, drug delivery systems,toners, catalysts, reagents, media for growth of biological material,supports, filtering devices, micro reactors, storage devices and otherrelated technologies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The selection of the porous material and the modifying agent will dependon the desired result. Thus, the porous material may be selected so thatit has hydrophobic groups in its pores, which groups can be changed bythe modifying agent to be hydrophilic groups in all but the smallestpores. Alternatively, the porous material may be selected so that it hashydrophilic groups within its pores, which can be changed by themodifying agent to be hydrophobic groups in all but certain sized pores.In conjunction with choosing the porous material the modifying agentmust also be chosen to produce a certain result. The modifying agentmust be chosen so that it is capable of reacting with, or catalyzing,the reaction of the reactive groups in the pores of the porous material.Relatively large (molecular size) modifying agents may be used insituations wherein it is desired to only modify the surfacecharacteristics of the larger pores in the porous material.Alternatively, a relatively small modifying agent may be used insituations wherein it is desired to modify the majority of the pores inthe porous material. The degree of chemical modification and the size ofpores modified can, by this preselection technique, be controlled toproduce a predesigned porous material intended for a particular end use.

A large variety of porous materials may be employed in the process ofthe present invention, wherein each porous material has pores of atleast two different size ranges and all of those pores are substantiallyhomogeneously distributed throughout the material. Suitable porousmaterials include macroporous polymers such as polymers of glycidylmethacrylate or acrylate; 2-hydroxyethyl methacrylate or acrylate; allylmethacrylate or acrylate; chloromethylstyrene;4-tert-butoxycarbonyloxystyrene; vinylacetate; vinylacetals; vinylalcohol, vinylbenzyl alcohol or vinyl phenol and esters or ethersthereof; 4-nitrophenyl acrylate; 2,4,5-trichlorophenyl acrylate;acryloyl succinimide; maleic acid; vinylbenzaldehyde, acrolein, ormethacrolein or acetal, imine, oxime, or hydrazone derivatives thereof;crosslinked with any of divinylbenzene; ethylene dimethacrylate oracrylate; diethylene glycol methacrylate or acrylate; divinylpyridine;bis- N-vinyl-2-pyrrolidone; N,N-methylene-bis-acrylamide; ortrimethylolpropane trimethacrylate. Other suitable porous materials arebased on natural polysaccharides such as cellulose, chitin, agarose,guar, and dextran. The porous material may also be an inorganic oxidesuch as silica, titania, zirconia, alumina, magnesia, and porous glass.Other suitable porous materials include bonded reactive phase materialsprepared by the reaction of an inorganic oxide with a reactivesilylation agent such as 1-glycidoxypropyl-trimethoxysilane,vinyltrimethoxysilane, and other silanes. The medium pore size of suchporous materials is from about 2 to about 100 nm. The pore sizedistribution generally ranges from about 1 to about 1500 nm. The porousmaterial may be of any suitable shape such as beaded (spherical),irregular, rod shaped, flat membrane-like or any other continuous shape.These porous materials are either commercially available from sourcessuch as Rohm and Haas, Mitsubishi, Dow, Bio-Rad, and Merck, or may beprepared by techniques known in the art such as disclosed in U.S. Pat.No. 5,130,343, the subject matter of which is incorporated herein byreference.

U.S. Pat. No. 5,130,343 discloses a procedure for manufacturingmacroporous polymers wherein the porogenic agent is a solution of asoluble linear polymer in a solvent which is a non-solvent for themacroporous polymer. The process of pore formation disclosed in U.S.Pat. No. 5,130,343 is initiated by a separation of the solid phase fromthe original single liquid phase, which can be initiated by crosslinkingduring polymerization, by crosslinking of already existing solublepolymeric chains, or by a precipitation stimulated by a chemicalreaction. These phase separation processes are random processes thatstart at the same time in many places within the original liquid andresult in the formation of spherical nuclei. These nuclei grow untilthey contact each other and build an array with the remaining solventwithin the voids of the enlarged nuclei. The array of spherical entitiesis then sintered to a mechanically strong porous solid using a meansrelevant to the particular material. The natural randomness of thenucleation results in a random pore distribution within the material.Further, since all of the porogenic material is present in thepolymerization mixture prior to the commencement of polymerization, allpores which are formed are uniformly distributed throughout theresultant polymers. Such macroporous polymers as well as porousmaterials based on natural polysaccharides and inorganic oxides that maybe prepared by known techniques, or obtained from numerous vendors,constitute a group of materials with a similar uniform distribution ofpores within their respective bodies.

Each porous material contains particular reactive groups within itspores. Depending upon the porous material, the reactive groups caninclude epoxy, alcohol, acetal, aldehyde, chloromethyl, thiol, amine,ester, carbonate, carboxylic acid, amide, oxime, imine, hydrazone,enamine, oxazoline or carboxylic anhydride groups. The reactive groupswill determine which modifying agents need to be used to modify thereactive groups to obtain the desired surface functionality of the poresin the porous material. The final surface functionality depends on thereaction scheme used to produce the final surface groups and to a lesserextent the initial surface groups. Example of suitable reaction schemesare disclosed hereinafter. Surface groups according to the presentinvention may have functionalities that include hydrophobic,hydrophilic, anion-exchange, cation-exchange, affinity, charge transfer,catalytic and metal ion complexing.

The modifying agents are selected by their size and ability to reactwith or catalyze the modification of reactive groups in the pores of theporous material. The size of the modifying agent is selected based onthe pore sizes of the porous material containing reactive groups to bemodified. Suitable modifying agents for larger pores, e.g. greater thanabout 10 nm, include polymeric catalysts such as poly(styrenesulfonicacid), poly(methacrylic acid), poly(acrylic acid), poly(vinylbenzoicacid), or a peracid thereof; poly(ethyleneimine) and its quaternizedderivatives, poly(triethylaminoethyl methacrylate), polyvinylpyridineand its quaternized derivatives, or poly(trimethylaminomethylstyrene)and polymeric reagents including a polymeric carbodimide or similarpolymeric coupling agent; a polymeric dimethylaminopyridine or similaracylation agent, polymeric amine or other polymers containing basicsubstituents. Suitable modifying agents for smaller pores, e.g. about 1to about 10 nm, include such as sulfuric acid, sodium hydroxide,triethylamine, dimethylaminopyridine. The small pore agents will becapable of modifying not only the small pores but also the large pores.

It is well known that the size of a polymer molecule in solution or itshydrodynamic volume, i.e. the volume it occupies in solution, varieswith its molecular weight and with the solvent used. (P. J. Flory,Principles of Polymer Chemistry, Cornell University Press, 1953); (G.Allen and J. Bevington, Eds., Comprehensive Polymer Science, PergamonPress, 1989, Volume 2, p. 199)

In the case of the reagent, the reagent reacts with the reactive groupsin the pores of the porous material into which it enters to change themchemically into different surface groups. The catalyst on the other handfunctions by catalyzing the reaction of the reactive groups with areagent present in the pores. For example, if the surface of the porescontain reactive epoxy groups and if the catalyst is a polymeric acid inwater, the epoxy groups will react with water in a hydrolysis reactionthat will transform the epoxy groups into diol groups only when thecatalyst is present. In the areas where the polymeric acid catalyst isnot present (small pores because of size constraints), the epoxy groupswill not react with water since the hydrolysis reaction cannot occur inthe absence of the catalyst. After the modification of the desired poresis finished, the catalyst is washed out of the pores and may be reusedfor a subsequent modification.

A few particular process schemes which are within the scope of thisinvention are described hereinafter. Though numerous other reactionschemes are possible, the following schemes are shown to illustrate thebasic concepts of the present invention. Other reactions and specificExamples are contained in Examples Section hereinafter.

In Reaction Schemes 1A and 1B, a porous material is derived fromglycidyl methacrylate. Therefore, the reactive groups are epoxides. Inthis reaction, a catalyst containing strongly acidic sulfonic groups isused together with water as a reagent to transform the hydrophobic epoxygroups (I) to diol groups (II) which are more polar and hydrophilic.##STR1##

A polymeric catalyst such as poly(styrenesulfonic acid) containingstrongly acidic groups, having molecular weight of over one million maybe used as the modifying agent. The polymeric acid used for themodification is unable to penetrate the pores having a size smaller thanits molecular size. When the hydrolysis is catalyzed with such apolymeric catalyst, the epoxide groups present in pores inaccessible tosuch a catalyst, i.e. the relatively small pores, remain unchanged andmay be used in further steps for other reactions.

If desired, the hydrophobicity of the pores containing the remainingepoxy groups can be increased, for example, by a reaction withrelatively small molecules such as higher alkylamines or dialkylamineswith alkyl groups containing at least about 8 carbon atoms (such asoctadecylamine), alkylarylamines or arylamines. The hydrophobicity andlow polarity of the long alkyl chain or aryl group in product IIIdominates over the polarity of the amino group.

On the other hand, reaction with an amine containing only short alkylchains such as reaction with diethylamine shown in Reaction Scheme 1Bresults in product IV with pronounced anion-exchange surfacefunctionality.

In Reaction Scheme 2, the starting porous material is again a copolymerof glycidyl methacrylate. In contrast to the polymeric catalyst, the useof aqueous sulfuric acid as a catalyst in the first reaction step of theconvergent approach causes hydrolysis of all epoxide groups present,even those in the smallest pores. The product is treated treated withbenzaldehyde under catalysis of a polymeric acid in the absence ofwater. The large polymeric catalyst does not penetrate the pores smallerthan its molecular size and the hydrophilic vicinal diol groups in smallpores remain unchanged. The resulting porous material possesses surfacefunctionality opposite to that produced in Reaction Schemes 1; with thesmall pores being hydrophilic while the large pores are hydrophobic.

Further treatment of the modified porous material with a polymeric acidin presence of water causes hydrolysis of benzylidene acetal groups V tooriginal vicinal diol groups. ##STR2## Assuming that the polymericacidic catalyst PA 1 has molecular volume smaller than PA 2 (M_(PA) 1<M_(PA2)), the acetal groups located in medium sized pores will survivethe treatment and a material appears which has three different zones,i.e. small pores hydrophobic, medium pores hydrophobic and large poresagain hydrophilic.

In Reaction Scheme 3, the porous material based on glycidyl methacrylateis again hydrolyzed in presence of aqueous sulfuric acid and the diolgroups are reacted with benzaldehyde in the presence of sulfuric acidunder anhydrous conditions. The next step is hydrolysis of thebenzylidene acetal groups catalyzed by polymeric catalyst. The acetalgroups in pores smaller than the size of the catalyst molecule remainunchanged while the others are transformed to a diol, making the largerpores hydrophilic. Finally, the hydroxyl groups in large pores reactwith chloroacetic acid in the presence of aqueous sodium hydroxide,producing cation exchange groups. The net result is that the smallerpores contain hydrophobic benzylidene acetal groups and the larger porescontain cation exchange groups. ##STR3##

In each of Reaction Schemes 1A, 1B, 2, and 3, the porous materialdescribed is based on glycidyl methacrylate. However, the composition ofthe porous material is not crucial to the final product. Rather, thesize of the pores, the pore size distribution and the surface groupswithin of pores of the starting porous material are more critical to thefinal product.

In Reaction Scheme 4, the starting porous material is irregular silica.As was the case for Reaction Scheme 1, the polymeric catalyst used as acatalyst in the first reaction step causes hydrolysis of all epoxidegroups unless they are hidden in smaller pores inaccessible to thepolymeric catalyst. Thus, the larger pores become hydrophilic. In thenext step, the remaining epoxide groups react with iminodiacetic aciddiethylester producing hydrophobic groups in the smaller pores. Theproduct is then treated with poly(N,N-diethyl-vinylbenzylamine) having amolecular size smaller than that of the polymeric acid used in the firstmodification step. The ester groups in pores accessible for the saidpoly(N,N-diethyl-vinylbenzylamine) are saponified to negatively chargedcarboxylic groups. The small pores remain hydrophobic while the mediumsize pores have typical ion-exchange properties. ##STR4##

The porous materials produced by the process of the present inventionhave many uses. They are particularly useful as separation media inliquid chromatography. For example, beads modified in the way depictedin Reaction Scheme 1A may be used in separating drugs from blood plasma.The blood proteins cannot bind to the hydrophobic octadecyl groups insmall pores because they cannot fit into those pores. The protein alsodo not bind to the hydrophilic surface of larger pores into which theyfit. On the other hand, smaller drug molecules also do not bind to thehydrophilic surface but they fit into and bind in the smaller pores.They are released when the surrounding liquid is changed to another onewhich breaks the interaction of the small molecules and the surfacehydrophobic groups.

The selectively pore-size modified porous beads are also useful as apacking in devices for blood perfusion after endo- or exogenouspoisoning of the living body. The low molecular weight toxic compoundbind to groups in smaller pores while the blood particles (ethyrocytes,leukocytes, platelets, etc.) do not penetrate into the beads at all andthe blood proteins (albumin, IgG) fit only into the larger hydrophilicpores. The separation of the toxic compounds is very selective as thegroups located in smaller pores may be specially designed to bind onlythe poison molecules. Thus, for removal of heavy metals, such asmercury, cadmium, or lead, the groups in smaller pores are iminodiaceticacid groups, thiol groups, ethylenediamine groups, etc.

The process of present invention is further described in the followingExamples which are recited herein as illustrative of the presentinvention but in no way limit the present invention. All parts andpercents are by weight unless otherwise specified.

EXAMPLES 1-3

Uniformly sized porous poly[glycidylmethacrylate-co-ethylenedimethacrylate] (GMA-EDMA) particles 10 μm indiameter were prepared by the modified activated two-step swelling andpolymerization method similar to that described in U.S. Pat. No.5,130,343 except for the addition of a mixture of cyclohexanol anddodecanol as porogen instead of the polymeric porogen. Pore sizedistribution was controlled by addition of butanethiol to the mixtureprior to the last polymerization step. The amount of butanethiol addedand the properties of the porous beads are summarized in Table I.

The content of epoxide groups was determine chemically as follows. Thebeads were dispersed in solution of tetraethylammonium bromide in aceticacid and titrated with 0.1 mol/l perchloric acid solution to theblue-green end point of crystal violet indicator. This technique isdescribed in detail in R. E. Burger and B. P. Geyer, in G. M. Kline,Analytical Chemistry of Polymers, Interscience, New York, 1959, p. 124.

Specific surface area and pore size distribution, characterized in theTable I by a median value, were determined by dynamic nitrogendesorption (BET). Pore size distribution and specific pore volume weredetermined by inverse size-exclusion chromatography (SEC) similar tothat used by I. Halasz and K. Martin, Angew, Chem., Int. Ed. Engl., 17(1978) 901.

                  TABLE I                                                         ______________________________________                                        Properties of Monosized Poly[Glycidyl Methacrylate-co-Ethylene                Dimethacrylate] Porous Beads                                                               Example 1                                                                             Example 2 Example 3                                      ______________________________________                                        Butanethiol added, wt %                                                                      0         0.6       1.2                                        Epoxy groups, mmol/g                                                                         2.7       2.1       2.0                                        Specific surface area                                                                        114.0     26.0      1.0                                        (BET), m.sup.2 /g                                                             Medium pore size diameter                                                                    10.9      6.4       --                                         (BET), nm                                                                     Specific pore volume                                                                         1.1       1.0       1.0                                        (SEC), ml/g                                                                   Polystyrene exclusion                                                                        340,000   77,000    31,000                                     limit (SEC)                                                                   ______________________________________                                    

All three kinds of polymer beads (10 g) were suspended separately in 50ml 0.1 mol/l sulfuric acid and kept at 60° C. for 10 hours while stirredoccasionally. All epoxide groups in the beads were hydrolyzed duringthis procedure as documented by the disappearance of the typical bandsof the epoxide groups at 1060, 906, and 852 cm⁻¹ and by an increase ofthe broad hydroxyl band at 3490 cm⁻¹ in IR spectrum.

This modification does not exhibit any pore-size selectivity.

EXAMPLES 4-6

The beads containing epoxide groups prepared in Examples 1-3 werehydrolyzed using acids with different molecular weights. The beadscontaining epoxide groups (0.2 g) were placed in a 50 ml beaker, 10 mlof 1 wt. % aqueous solution of polymeric acid was added and the beakerwas sealed with Parafilm. The dispersion was stirred at room temperaturefor 48 hours. The beads were filtered off on a fritted glass and washedwith water to the neutral reaction of the filtrate, washed with acetoneand dried. The content of the remaining epoxide groups in the beads wasdetermined by a method described in Examples 1-3. Table II shows theextent of pore-size selective reaction by providing the percentage ofremaining epoxide groups located in the polymer beads prepared accordingto Examples 1, 2 or 3 and used in Examples 4, 5 and 6, respectively,after pore-size sensitive hydrolysis was performed.

                  TABLE II                                                        ______________________________________                                        Percentage of Remaining Epoxide Groups in Porous                              Poly[Glycidyl Methacrylate-co-Ethylene Dimethacrylate] Beads                  after Hydrolysis Catalyzed by a Polymeric Acid                                % Remaining Epoxide Groups                                                    Catalyst  Example 4   Example 5 Example 6                                     ______________________________________                                        PSSA 5    45          57        68                                            PSSA 47   64          81        88                                            PSSA 400  81          96        97                                            PSSA 1200 89          98        97                                            ______________________________________                                    

PSSA 5 is poly(styrenesulfonic acid) having a molecular weight of 5,000.PSSA 47 is poly(styrenesulfonic acid) having a molecular weight of47,000. PSSA 400 is poly(styrenesulfonic acid) having a molecular weightof 400,000. PSSA 1200 is poly(styrenesulfonic acid) having a molecularweight of 1,200,000. All the polymeric catalysts had very narrowmolecular weight distribution as documented by the polydispersity index,i.e., the ratio of the weight average molecular weight and numberaverage molecular weight M_(w) /M_(n), which was less than 1.1 in allpolymeric acids used.

Table II shows clearly the size-selectivity of the hydrolysis, theextent of which depends both on the molecular weight of the catalyst andon the pore size distribution of the modified polymer.

The remaining epoxide groups located in smaller pores were used forfurther modification reactions with octadecylamine or diethylamineaccording to the Reaction Scheme 1A and 1B. In the former case, the drybeads obtained in Example 4 after hydrolysis catalyzed bypoly(styrenesulfonic acid) PSSA 47 were admixed to a melt of 1 goctadecylamine and heated to 70° C. for 16 hours. The mixture wasdiluted with 2 ml dioxane, mixed 1 hour, and the beads filtered off.Then they were washed consecutively with dioxane, water and methanol anddried. In this way, pores with a size larger than the molecular size ofPSSA 47 in water contain hydroxyl groups and are hydrophilic while poressmaller than that limit contain 0.35 mmol/g of attached octadecylaminegroups with typical hydrophobic character.

The latter modification proceeded in 2 ml diethylamine using beads fromExample 5 hydrolyzed with PSSA 37 and PSSA 5, respectively.

The diethylamino group content was 1.9 and 1.3 mmol/g, respectively. Thediethylamino groups located in pores smaller than the molecular volumeof the polymeric acids used for the hydrolysis in the first reactionstep have an anion exchanger character and thus the pores are more polarand can be used in traditional ion exchange. Pores larger that thosemodified with diethylamino groups are hydrophilic as they contain onlyhydroxyl groups resulting from hydrolyzed epoxides.

EXAMPLES 7-8

Diol beads prepared according to Example 1 and 2, respectively, (10 g)were suspended in 200 ml toluene containing 13.4 g benzaldehyde and 0.18g 4-toluenesulfonic acid. The mixture was refluxed for 48 hours whilethe water produced by the reaction was continuously removed. The beadswere separated, washed consecutively with toluene, acetone and methanoland dried.

Beads containing benzylidene acetal groups (200 mg) were suspended in a1:1 mixture of dioxane and 0.1 mol/l aqueous sodium sulfate and 10 ml of1 wt. % aqueous solution of the catalyst was added. The mixture wasrefluxed for 60 hours. The pore selective modified beads were separated,washed with water and methanol and dried. The extent of the reactioncatalyzed by different polymeric acids as determined by IR spectroscopyis summarized in Table III.

                  TABLE III                                                       ______________________________________                                        Percentage of Remaining Benzylidene Acetal Groups in Modified                 Porous Poly[Glycidyl Methacrylate-co-Ethylene Dimethacrylate]                 Beads after Hydrolysis Catalyzed by a Polymeric Acid                          % of Remaining Benzylidene Acetal Groups                                      Catalyst       Example 7 Example 8                                            ______________________________________                                        PSSA 5          7        22                                                   PSSA 47        15        48                                                   PSSA 400       24        89                                                   PSSA 1200      47        95                                                   ______________________________________                                    

The polymeric acids used in these Examples are identical with those usedin Examples 4-6. In Examples 7 and 8 again the extent of the reactionsdepends both on the molecular weight of the catalyst and on the poresize distribution of the modified polymer.

Beads containing benzylidene acetal groups (200 mg) were suspended in a1:1 mixture of dioxane and 0.1 mol/l aqueous sodium sulfate and 10 ml of1 wt % aqueous solution of the catalyst was added. The mixture wasrefluxed for 60 hours. The pore selective modified beads were separated,washed with water and methanol and dried. The extent of the reactioncatalyzed by different polymeric acids as determined by IR spectroscopyis summarized in Table III.

In the carboxymethylation, the previously modified polymer in a 25 mlvial was suspended in a solution 0.4 g sodium hydroxide in 0.8 ml water,and a solution of 0.3 g chloroacetic acid and 0.4 g potassium iodide in0.2 ml water was added with stirring at room temperature. Thetemperature was raised to 60° C. and the mixture was stirred for aperiod 3 hours. The product was transferred in a beaker and thoroughlywashed with water several times.

The reaction path is shown in Reaction Scheme 3. Beads from Example 7were partly hydrolyzed with PSSA 47 as a catalyst. All groups in poreslarger than the molecular size of the polymeric acid in water were firsttransformed into hydroxyl groups and then to carboxymethyl groups. Thefinal product contained again hydrophobic benzylidene groups in poressmaller than the molecular size of the poly(styrenesulfonic acid) PSSA47 in water while the groups located in larger pores were negativelycharged carboxylates with a typical cation exchanger character.

EXAMPLES 9-10

Diol beads prepared according to Examples 1 and 2, respectively, (0.5 g)were suspended in 10 ml dihydropyran containing 0.08 g 4-toluenesulfonicacid. The mixture was refluxed for 8 hours and cooled. The beads wereseparated, washed consecutively with dioxane, acetone and methanol, anddried.

Beads containing tetrahydropyranyl ether groups (200 mg) were suspendedin a 1:1 mixture of dioxane and 0.1 mol/l aqueous sodium sulfate and 10ml of 1 wt. % aqueous solution of the catalyst was added. The mixturewas refluxed for 30 hrs. The pore-selective modified beads wereseparated, washed with water and methanol, and dried. The extent of thereaction catalyzed by different polymeric acids as determined by IRspectroscopy is summarized in Table IV.

                  TABLE IV                                                        ______________________________________                                        Percentage of Remaining Tetrahydropyranyl Ether Groups in                     Modified Porous Poly[Glycidyl Methacrylate-co-Ethylene                        Dimethacrylate] Beads after Hydrolysis Catalyzed by a polymeric               Acid                                                                          % of Remaining Tetrahydropyranyl Ether Groups                                 Catalyst       Example 9 Example 10                                           ______________________________________                                        PSSA 5         18        29                                                   PSSA 47        25        51                                                   PSSA 400       33        88                                                   PSSA 1200      53        96                                                   ______________________________________                                    

The polymeric acids used in this Example are identical with those usedin Examples 4-6. Also in Examples 9 and 10, the extent of the reactiondepends both on the molecular weight of the catalyst and on the poresize distribution of the modified polymer.

EXAMPLE 11

A copolymer of styrene, 4-vinylbenzyl chloride and divinylbenzene wasprepared by a standard suspension polymerization. A mixture containing25 ml styrene, 25 ml 4-vinylbenzylchloride and 50 ml divinylbenzene(technical grade), 1 g azobisisobutyronitrile, and 100 ml toluene wasdispersed in 300 ml of aqueous solution of polyvinyl alcohol. Themixture was stirred for 10 minutes with an anchor shaped stirrer at roomtemperature. The temperature was then increased to 70° C. and thepolymerization continued for 24 hours to afford porous beads with a meansize of 0.18 mm. The porous beads were separated by sedimentation anddecanted 3 times in 500 ml distilled water. The washing procedurecontinued in methanol, toluene, and methanol again, and the beads weredried. The chlorine content in the beads was 5.5 wt % as determined byelemental analysis. The medium pore size was 135 nm and the porosity54%, both according to mercury porometry measurement. The specificsurface area was 120 m² /g as determined by BET measurements.

The beads containing chloromethyl groups (1 g) were refluxed for 96hours in 10 ml tetrahydrofuran solution of the sodium salt preparedseparately by reaction of sodium hydride (50% w/w in paraffin oil, 0.1mmol) with a tetrahydrofuran solution of 1 g/l poly(ethylene oxide),(molecular weight 100,000 daltons). After washing with tetrahydrofuran,methanol, water, the beads were transferred to 5 ml 33% aqueous solutionof trimethylamine and kept at 50° C. for 10 hours.

The larger pores of the resulting porous polymer are covered withhydrophilic polyethylene oxide chains while the smaller pores containstrong anion exchange quaternary ammonium groups.

EXAMPLE 12

A mixture of 4 ml of freshly distilled methacrolein, 4 ml technicaldivinylbenzene, 0.8 g benzoylperoxide, and 12 ml cyclohexanol wasdeaerated by purging with nitrogen and heated in a sealed stainlesssteel (10 mm I.D.) tube for 20 hours. The polymer block was crushed in amortar and extracted with toluene, methanol and toluene again using aSoxhlet apparatus.

The porous polymeric material (1 g) was transferred into a 50 ml roundbottom flask and 20 ml toluene solution containing 2 g 1,2-dodecanedioland 20 mg 4-toluenesulfonic acid was added. The contents of the flaskwere refluxed for 60 hours and the released water was removedcontinuously. The product was washed in the flask by decantation intoluene, methanol, and water. The treatment caused a large decrease ofthe band at 1720 cm⁻¹ in the IR spectrum. This band is characteristic ofthe aldehyde groups of polymerized methacrolein.

The pore-selective hydrolysis of acetal groups was catalyzed bypoly(styrenesulfonic acid) with a molecular weight of 1,200,000 as inExample 7 and a rough estimate of the remaining acetal groups was 50% ofthe original amount.

The aldehyde groups located in larger pores were reduced by sodiumborohydride to hydroxyl groups rendering the larger pores morehydrophilic. At the end, the porous material contained hydrophobicchains in its small pores and hydrophilic groups in its larger pores.

EXAMPLE 13

To 1 g silica in the form of irregular particles having sizes from about5 to 25 mm, with specific surface area 500 m² /g (BET), pore volume 0.75ml/g, and average pore diameter 6 nm, 8 ml of water containing 2 ml1-glycidoxypropyl-trimethoxysilane was added. The mixture was placed in75° C. water for 2 hours, the modified silica was filtered off, washedwith water and dried. The product contained 0.15 mmol epoxide groups/g.

The particles were treated with 2 ml 1 wt % aqueous solution ofpoly(styrenesulfonic acid) PSSA 47 (molecular weight 47,300) in the samemanner as described in Example 5. After the hydrolysis of the epoxidegroups in the larger pores to hydrophilic diol functionality wasfinished, the content of remaining epoxide groups in the porousparticles was 73% of the original amount. Residual epoxides were thenreacted with iminodiacetic acid diethyl ester (IADE). The particles (0.2g) were suspended in 1 ml 10 vol. % solution IADE in dioxane and heatedto 70° C. for 24 hours.

Partial hydrolysis of the ethyl acetate groups was catalyzed bypoly(N,N-diethylvinylbenzylamine) with a molecular weight of 8,000. Theparticles were admixed to a 1 wt. % THF- water solution ofpoly(N,N-diethylvinylbenzylamine) and heated in the water bath 24 hoursto 60° C. During this reaction approximately 50% of ester groups werehydrolyzed to produce about 0.1 mmol/g of negatively charged carboxylgroups while leaving about 0.05 mol/g hydrophobic diaminoacetate groupsunchanged. The whole reaction path is shown in Reaction Scheme 4.

What is claimed is:
 1. A selectively modified material comprising aporous material having pores of at least two different size ranges, withthe pores of one size range having surface groups of one functionalityand the pores of another size range having surface groups of a differentfunctionality wherein the pores are substantially homogeneouslydistributed throughout the material.
 2. The material of claim 1, whereinthe porous material has pores of five different pore size ranges, withthe pores of each pore size range having different surface groups withdifferent functionalities compared to all of the other surface groups.3. The material of claim 1, wherein the functionalities are selectedfrom any of hydrophobic, hydrophilic, anion exchange, cation-exchange,affinity, charge transfer, catalytic, and metal ion complexing.
 4. Thematerial of claim 1, wherein the porous material contains pores of twodifferent size ranges with one size range having surface groups of onechemical composition and the pores of another size range having surfacegroups of a different chemical composition.
 5. The material of claim 1,wherein the two different functionalities are hydrophobic andhydrophilic.
 6. The material of claim 1, wherein the two differentfunctionalities are of differing polarities.
 7. The material of claim 1,wherein the two different functionalities are hydrophobic andcation-exchange.
 8. The material of claim 1, wherein the two differentfunctionalities are hydrophilic and anion-exchange.
 9. The material ofclaim 1, wherein the porous material is a polymer selected from thegroup consisting essentially of glycidyl methacrylate or acrylate;2-hydroxyethyl methacrylate or acrylate; allyl methacrylate or acrylate;chloromethylstyrene; 4-tert-butoxycarbonyloxystyrene; vinylacetate;vinylacetal; vinyl alcohol, vinylbenzyl alcohol or vinyl phenol andesters or ethers thereof; 4-nitrophenyl acrylate; 2,4,5-trichlorophenylacrylate; acryloyl succinimide; maleic acid; vinylbenzaldehyde,acrolein, or methacrolein or acetal, imine, oxime, or hydrazonederivatives thereof; crosslinked with any of divinylbenzene; ethylenedimethacrylate or acrylate; diethylene glycol methacrylate or acrylate;divinylpyridine; bis-N-vinyl-2-pyrrolidone;N,N-methylene-bis-acrylamide; or trimethylolpropane trimethacrylate. 10.The material of claim 1, wherein the porous material is an inorganicoxide.
 11. The material of claim 1, wherein the inorganic oxide isselected from the group consisting of silica, titania, zirconia,alumina, magnesia or glass.
 12. The material of claim 1, wherein theinorganic oxide porous material is a reaction product of the inorganicoxide and a silylation agent.
 13. The material of claim 1, the whereinporous material is a natural polysaccharide porous polymer.
 14. Thematerial of claim 13, wherein the porous polysaccharide polymer isselected from the group consisting of cellulose, chitin, agarose,dextran, mannan, guar.